Helicopter lighting

ABSTRACT

Relatively rotatable elements coupled for light transmission by fiber optic devices analogous to electrical commutators. A rotary wing aircraft embodiment employing fiber optics in the rotor blade for navigational lights has a flexible light pipe extension from the blade with an end fixed to move with the driving assembly in a set circular path, to sweep by and pick up light from a light source on the body. Other portions of the extension flex to follow cyclic pivoting of the blade relative to its driving assembly. Fibers in the blade are arranged to bend with the blade during operation by use of a flexible light pipe within which the fibers adjust relative to one another during blade bending. Heat-curing of plastic about a heat resistant flexible light pipe and bonding the fibers directly into the blade matrix as bendable strength element using a thin, wide and long ribbon of optical fibers are shown. Light sources on the body of the aircraft are shown as fiber light pipes with ends fixed to be swept by the pickup pipes. Four source light pipes provide light in accordance with navigational rules, a rotor blade receiving alternately white, green, white, red light as it rotates through various sectors. A Maxwellian lens at the end of a source light pipe defines an extended lighted arc along the pickup path, to provide extended duration of light transmission in each sector, the lens also enabling variation in the physical position of the blade assembly as occurs in the field.

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Van Iderstine et al. SUBSTETW-E I [451 M31? 1973 s41 HELICOPTER LIGHTING57 ABSTRACT [75] Inventors: Theodore J. Van lderstine, Peabody;Relatively rotatable elements coupled for light trans- Leonard J.Bonnell, Medford, bo mission by fiber opticdevices analogous toelectrical of Mass. commutators.

[73] Assignee: Dyonics, Incorporated, Woburn, A rotary wing aircraftembodiment employing fiber Mass. optics in the rotor blade fornavigational lights has a flexible light pipe extension from the bladewith an 70 [22] Filed Sept 19 end fixed to move with the drivingassembly in a set [21] Appl. No.: 72,010- circular path, to sweep by andpick up light from a light source on the body. Other portions of theextenflex to follow cyclic pivoting of the blade relative 52 us. c1...240/7.7, 244/1111 511 lnt.Cl. ..B64d 47/02 to dmmg assembly" Fbersblade are ranged to bend with the blade during operation by use [58]Feld Search z gfi g'b 55 22,; of a flexible light pipe within which thefibers adjust relative to one another during blade bending. Heatcuringof plastic about a heat resistant flexible light I pipe andbonding thefibers directly into the blade UNITED STATES PATENTS matrix as bendablestrength element using a thin, wide and long ribbon of optical fibersare shown. Light sources on the body of the aircraft are shown as fiber[56] References Cited 2,290,278 7/1942 Failla ..l 16/129 L light pipeswith ends fixed to be swept by the pickup 213331492 11 1943 Ridge ..2401E pipes. Four source light i es provide light in accordance withnavigational rules, a rotor blade receiv- OTHER PUBLICATIONS ingalternately white, green, white, red light as it rotates through varioussectors. A Maxwellian lens at the end of a source light pipe defines anextended lighted arc along the pickup path, to provide extended durationof light transmission in each sector, the lens also enabling variationin the physical position of the blade assembly as occurs in the field.

Concepts of Classical Optics, Strong, 1958, pp. 562-565, QC 355077 C.Z.

Primary Examiner-S. Clement Swisher Assistant Examiner-Daniel M. YasichAttorney-John N. Williams 27 Claims, 20 Drawing Figures PATENTEDMARZ'!I975 SHEU 2 BF 5 FIG 5 FIG 20 PATENTEU MAR 2 7 I973 3.723722 SHEET 5 OF5 HELICOPTER LIGHTING This invention relates generally to illuminationof rotary elements and in particular to lights on helicopter blades e.g.to provide sector coding, such as providing red and green running lightsfor blades when on the port and starboard sides of the fuselage,respectively, using fiber optics.

Fiber optics are known and have been suggested by others as substitutesfor existing lighting, including use on rotary devices and helicopterblades. Practical application of fiber optics to such rotary deviceshowever encounters numerous and to an extent apparently conflictingproblems. It is an object of this invention to resolve these problemsand provide practical and improved lighting of rotary members,especially helicopter blades, employing fiber optics.

Among the objects of the invention are to provide apparatus fortransmitting light to rotary structures, I

determined by blade position, over a substantial portion of eachrevolution and when desired, without being visible from certain selecteddirections.

With particular reference to the problem of providing reliable andefficient navigational lighting for helicopter rotor blades, theinvention features a set of optic fibers extending along the length of ablade, secured against lengthwise movement and held in a manner topermit their bending transversely to accommodate vertical bending of theblade during operation and a flexible light pipe extension includinglight conducting fiber portions disposed in a flexible casing andextending from the inboard portion of the blade and in light supplyingrelationship to the optic fibers. The light pipe extension is mounted torotate with the blade about the blade drive axis and to flex withrepeated cyclic pivoting of the blade about the blades longitudinal axisand has an end portion adapted to be held in a predetermined positionrelative to the rotating drive mechanism of the aircraft for describinga predetermined circular path to sweep by and pick up light from a lightsource on the body of the helicopter.

ln preferredembodiments the fibers extending. along the length of theblade form a flexible bundle housed in a flexible casing which isdisposed within the blade and secured against movement relative thereto;the internal cross-sectional area of the casing exceeds the aggregatecross-sectional area of the fibers of the bundle, providing room for thefibers to adjust themselves relative to one another during bending ofthe blade during operation; the light pipe extension is defined by anintegral extension of the fibers and easing that are within the blade;the optic fibers are glass fibers joined together at their outer endsinto a light transmitting end face by heat-resistant bonding materialand the casing is a heatresistant housing and the blade is constructedof aluminum skins permanently secured about the fibers and casing; theoptic fibers are embedded directly in a structural matrix defining aportion of the blade and secured in a manner to contribute structuralstrength to the blade; outboard portions of the fibers protrude beyondthe matrix into a housing and end portions of the fibers are bondedtogether to define an optical light transmitting face; inboard portionsof the fibers protrude beyond the matrix and form the optic fiberportions of the light pipe extension; the fibers are secured to eachother in the form of a flat ribbon bonded to other structural portionsof the blade, the ribbon extending in the direction of length of theblade with its width-wise direction extending in the direction betweenthe leading and trailing edges of the blade and the direction of itsthickness aligned with the direction of operational blade bend; and, aplurality of ribbons may be included as structural members of the blade.

With reference to the particular problem of providing the effectivetransmission of light between rotary and movable and stationary parts,the invention features the combination of two assemblies, one movablerelative to the other, and means for transmitting light from a sourcethrough both assemblies. This means includes first and second fiberoptic light pipes, each having input and output end surfaces, and onelight pipe is associated with each assembly. The input end surface ofthe first light pipe is arranged'to receive light from the source, theoutput end surface of the first light pipe defines an object plane, theinput end surface of the second light pipe defines an image plane andthe output end surface of the second light pipe is arranged to deliverthe transmitted light. The end surfaces defining the object plane andthe image plane are spaced apart and relatively movable between at leastone position in which they are disposed in light transmitting alignmentand at least one position in which they are out of light transmittingalignment and the combination also includes structure disposed betweenthe image and object planes and including a lens assembly with a lenswhich is spaced apart from one of the end surfaces defining one of theplanes and arranged to effectively focus light between the object planeand the image plane when the planes are in the light transmittingalignment. In preferred embodiments the lens is arranged to provide alight image having a depth of field sufiicient to permit variations intolerance of the relative positioning of the output end surface of thefirst light pipe and the input end surface of the second light pipewithout loss of the transmission of light from the source to the outputend surface of the second light pipe; the lens assembly has two lensesand is a Maxwellian field lens assembly; the lens assembly is arrangedto be adjusted to conform to the actual spacing between the output endsurface of the first light pipe and input end surface of the secondlight pipe after the assemblies have been assembled initially andthereby to effectively transmit light from the output end surface of thefirst light pipe to the input end surface of the second light pipe; thelens assembly is arranged to focus, in the direction of the image plane,light from the object plane over a region having a minimum dimension, in

the direction of relative movement, which is substantially greater thanthe corresponding dimension of the input end surface of the second lightpipe and the light transmitting alignment occurs when any portion of theregion and the input end surface of the second light pipe are aligned.

Other objects, features and advantages will become apparent from theabstract and from the following description of a preferred embodiment ofthe invention, taken together with the attached drawings thereof, inwhich:

FIG. 1 is a partially diagrammatic view in side elevation of ahelicopter incorporating the lighting system of the invention;

FIG. 2a is a top view of a rotor assembly showing the color pattern towhich the navigational lights on the rotor blades must conform duringeach revolution;

FIG. 2b is a cross-sectional view taken along line 2b-2b of FIG. 1; andFIGS. 20 and 2d are schematic views of the coupling assembly;

FIG. 3 is a detailed view in cross-section of the optical couplingassembly shown in FIG. 1;

FIG. 4 is a sectional view, taken along line 4-4 of FIG. 3, showing theend surface of a typical rotating light pipe and the image planeprojected thereon by the lens assembly;

FIG. 5 is a side elevation of an alternate embodiment of the opticalcoupling of the invention;

FIG. 6 is a cross-sectional view ofa rotor blade;

FIG. 7 is a longitudinal view, taken along line 7-7 in FIG. 6 andshowing a portion of the fiber optic pipe, of a rotor blade;

FIG. 8 is a longitudinal view of the outboard end of a rotor blade;

FIG. 9 is a longitudinal view, showing one method of entry of a fiberoptic pipe to and within a rotor blade, of the inboard end of a rotorblade;

FIG. 10 is a diagrammatic representation, showing two optic fibers, of aportion of a rotor blade in an unstressed condition;

FIG. 11a is a diagrammatic representation of the same portion of therotor blade after it has been deformed;

FIG. 11b is an enlarged view of a portion of the rotor blade shown inFIG. 11a;

FIG. 12 is a cross-sectional view of an alternate embodiment of theoutboard end of a rotor blade;

FIG. 13 is a cross-sectional view of the inboard end of the rotor bladeof FIG. 12 showing a second method of entry of a fiber optic pipe to andwithin the rotor blade;

FIG. 14 is a perspective view, partly broken away, of a fiber opticlight ribbon;

FIG. 15 is an enlarged detailed view of the portion of the ribbon ofFIG. 14 circumscribed by circle A;

FIG. 16 is a diagrammatic perspective view, partly broken away, of aportion of a rotor blade including a fiber optic light ribbon;

Referring to FIGS. 1 and 2, there is shown a helicopter 10 having acabin or body 12 with longitudinal axis 11 and being arranged to bepropelled vertically by rotor blades 14 and 16 which are rotatablymounted on a vertical drive shaft 18 driven by the helicopter motor (notshown), the shaft having axis 19. As is well known in the helicopterindustry, suitably adjustable connectors are also provided between shaft18 and rotor blades 14 and 16 and are arranged to pivot the blades abouttheir longitudinal axes to permit control of the pitch of rotor blades14 and 16 as they rotate around shaft 18.

The body 12 of helicopter 10 is provided with at least one suitable lamp20, and a plurality of fiber opfigll ht 35 220, b, c, and d,respectively, havirTg smooth polished end surfaces 24a, b, c, d,definingobject planes (to be discussed below) these end surfaces being fixedrelative to the body 12 of the helicopter. Each light pipe 22 isarranged to couple light from lamp 20 to its respective end surface 24,the latter being supported by a cylindrical housing 26 mounted by anysuitable means on cabin 12. Surfaces 24a, b, c, d (FIG. 2b) lie on thecircumference of a circle 28 of radius R which is concentric about theaxis 19. Through the use of appropriate filters (not shown) white lightis coupled to surfaces 24a and 24c, red light is coupled to surface 24dand green light is coupled to surface 24b. Each pipe 22 is provided witha Maxwellian lens assembly 30 (to be discussed in greater detail below)which is arranged to project the light coupled to end surfaces 24upwardly toward blades 14 and 16. Each of blades 14 and 16 has a fiberoptic light pipe 320 and 32b respectively disposed substantially withinblades 12 and 14 each with an integral flexible fiber optic extension34, secured to shaft 18, extending downwardly to an end surface 36 whichis fixed relative to drive shaft 18 and defines an image plane 38 (to bediscussed below) located a distance R from axis 19. Advantageously,light pipes 32a, 32b are threaded through and secured by any suitablemeans to an aluminum extrusion rotor blade frame with epoxy andfiberglass applied thereabout, aluminum skins are epoxied about theframe, and the blade is cured in an oven with the light pipe in place.Fiber optic pipes 32a and 32b are turned upwardly near the outboard endsor tips 40 of blades 14 and 16, respectively have upper end surfaces 42aand 42b, adjacent Fresnel lenses 44a and 44b mounted in the top surface46 of blades 14 and 16, and are arranged to couple light projected ontosurfaces 36 to upper surfaces 42a and 42b for display through lenses 44aand 44b respectively.

It will be seen, referring to FIG. 2c, that the interaction of therespective end surfaces 24 and 36 are somewhat analagous to anelectrical commutator. I-Iere only one end surface 24a is shown, fixedto the helicopter body 12 and only one end surface 36a is shown, movableabout axis 19. Light from the stationary element 24a is transmitted overan air gap to rotary element 36a which repeatedly sweeps past it alongpath 19a. The blade cyclically pivots about its own axis (FIG.2d), thusmoving relative to surface 36a, however upper parts of extension 34 flexas suggested in FIGS. 2c and 2d, to accommodate this pivoting, the endof the rotor blade being thus maintained in light transmittingcontinuity with surface 36a.

Referring now to FIG. 3, a typical Maxwellian lens 30 and itsrelationship to typical light pipe 22 and flexible fiber optic lightpipe extension 34 is shown in detail. Light pipes 22 and 34 respectivelyhave hose coverings 50 and 52, preferably constructed of stainless steelinterlocked flexible metal, disposed around glass optic fiber bundles 54and 56, respectively, which terminate in t hemTghly polishedefid'surfaces 24 and 36 respec- 64 and 66, spacer 68 and O-ring70 in place. Housing 5 26 is provided with a set screw 74 to lockassembly 30 in place at a desired adjustment.

When bundle 54 transmits light, the light emerges 1 from surface 24 inthe form of an exit cone 76. Lens assembly 30 reimages the light andfocuses the light uniformly and with a depth of field 77 ofapproximately one-fourth inch onto surface 36. The mounting of assembly30 on threads 58 permits adjustment of the lens assembly to provide thisdepth of field for any separa- 1 tion 78 (between the upper end 80 ofhousing 26 and surface 36) from 2 inches up to 10 inches.

The end surface 24 of illuminating bundle 54 is defined as the objectplane and the image plane 38 is the area where the illumination isuniform. This is located (FIG. 4) at the end surface 36 while itsdimension (M) in the direction of relative movement is approximately 8times larger than the diameter D of end surface 36. This dimension playsan important part in to provide navigational lights in accordance withnavigational regulations.

To explain this in more detail, the distance from end surface 24 to theaperture of lens assembly 30 is 11 the rear of the cabin, red light atthe position to the left of the cabin and green light at the position tothe right of the cabin. v

For a standard operational speed of rotation of 600 r.p.m. light will betransmitted to each lens 44 at each of the four positions approximately10 times per second and, therefore, a nearly continuous light willappear to the human eye at each position.

As is well known in the helicopter industry, the distances betweenmoving and stationary parts may vary considerably from the distanceswhen the helicopters are initially assembled at the factory. Thesevariations may be due to mechanical wear or to replacement of parts,often performed under considerable time pressure, in the field.Adjustable lens assembly 30 also accommodates these variations whileinsuring efficient transmission of light between end surfaces 24 and 36.

As is apparent, orientation of the surfaces 24 and 36 may be varieddepending upon the requirements of the particular aircraft.Advantageously, they will be parallel to each other, however, in orderto insure maximum efficiency in transmission of light. FIG. 5 shows onealtemate embodiment of the invention in which surfaces supplying lightto the blades for a sufficient time period 25 distance from the exitpupil 82 or aperture of lens assembly 30 to the image plane 38 is d,. Asan example of a practical embodiment of this invention, assume thatlight pipe extension 34 containing bundle 56 comes down along the rotorsupport shaft so that surface 36 is located 2 inches from the axis 19 ofthe drive shaft and 35 which forms a beam of light which is uniform overthe area defined as the image plane 38. If the dimensions. are chosen sothat the focal length of lens assembly 30 A is 1.12 inches, end surfaces24 and 36 are each onefourth of an inch in diameter, and distance a! is1 inch,

the image plane 38 will lie a distance d, of 8 inches beyond the exitpupil 82 of lens assembly 30 and will have a diameter or length 84 of 2inches in image plane 38. Therefore, as the bundle 56 with its surface36 in image plane 38 passes alohg th ir nage plane, illumina: tion willbe coupled from end surface 24 to end surface 36 and illum ihafad'ieih'ellens EZTFor-the dimensions which have been described, theangular time, on time, during which single bundle 56 couples illumination from a particular end surface 24 will be approximately Thus, for ahelicopter with two rotor blades, each with a bundle 56, and fourbundles 54 I mounted on the cabin 12 and spaced apart, the Fresnel lens44 on each blade will be illuminated four times during each revolution.As is shown in FIG. 2a by filtering the light transmitted from source 20toend surface 24b and to end surface 24d, white light may be transmittedto lenses 44 at the positions to the front and 24 and 36 are disposed invertical, rather than horizontal planes.

The light source 20 would normally be located somewhere within or on thecabin ceiling structure of the helicopter. It would be usually mostconvenient to mount lens assemblies 30 on the ceiling, although it ispossible that an extra length of light pipe 22 may be required in orderto locate the light source 20 in a lower position than the ceiling inorder to achieve proper weight distribution within the vehicle. Lightsource 20 should be located in such a position that the heat generatedby it will not cause any problems with other portions of the vehicle,that is it shouldnot be located directly adjacent to fuel or oil tanks,etc. In addition, it also must be located in such a position as to alloweasy change of the lamps. The light pipes 22 should be of such aconstruction as to resist vibration, but need not be extremely flexibleas it is not anticipated that it will be flexed regularly during itslifetime. However, its lifetime is expected to be extended and it mustbe protected from abuse occurring within the cabin, that is to saymechanical abuse.

According to the invention light pipe extension 34 is extremelyflexible, and flexes with the motion of the helicopter blades 14 and 16in normal flighta cyclical motion about a longitudinal blade axis tovary the angle of attack with relationship to the helicopter during eachcircular traverse. A continuation of the flexible light pipe through thelength of the blade accommodates bend of the blade along itslongitudinal axis (a flapping motion) which occurs at varying timesduring its operation. According to the invention each bundle allows forthese motions through a lifetime projected at approximately 15 to 20million cycles of blade rotation. The extension 34 is provided withsupport to remain clear of the mechanism for the rotor blade. Accordingto the invention this may be accomplished in a variety of ways dependingupon the particular installation;

however, for all configurations the inner end of the extension should berigidly disposed on the circle 28 (FIG. 2b) in light receiving relationto the illuminating source while the part of the extension between thisend and the blade must be free to flex. The portion of the light pipelocated within the helicopter blades 14 and 16-that is to say, theportion labelled 32-are, in the preferred embodiment, able to withstandthe temperatures of lamination of the blade without deterioration of thecovering of the bundle and the fibers in bundle 56 must remain free tomove within the bundle covering during flexure of the rotor blade at alltimes throughout the blade life. With reference to FIGS. 6 and 7, thereis shown a typical fiber bundle $6 with its covering 88 in a helicopterrotor blade 90. The outer covering 88 and the bundle 86 are secured tothe blade, for example, by the epoxy 91 shown, so that there is nomotion of the light pipe with respect to the center of gravity or centerof lift of the rotor blade during its operation. The rotor blade whichmay turn as fast as 600 to 700 rpm. develops a considerable centrifugalforce at or near the outboard end or tip 92, but the secured light pipedoes not change the weight distribution. However, according to theinvention the individual glass fibers are not so secured, and flexduring flight, adjusting themselves within the open space of the casing,as the helicopter rotor blade 90 flexes along its longitudinal axis.That is to say, the outboard tip 92 moves up and down in a mannersimilar to the flapping of a bird's wing. This motion is effectively abending of the blade itself. In addition to the up-and-down motion theblade 90 tends to fly"that is, the pitch of the blade is changed bymechanisms to effect flight and the forces caused thereby tend tomaintain the tip 92 in a constant attitude so that there is a torsionalchange in the lay of the blade with time. When tip 92 of the blade movesup and down the blade tends to take on a curved shape (see FIGS. 10, 11aand 11b). This curving causes the outer surface 94 of the blade on theoutside of the curve to become longer than the inner surface 96 of theblade on the inside of the curve. The fibers (two typical fibers,designated 98 and 100 are shown) at this same time, then reach acondition in which the path length has increased for the fiber 98 whichis nearer the outside surface 96 of the curved blade. By allowing thefibers 98 and 100 to remain free and to move to a limited extent withinthe covering 98 rather than the curving causing a change in their pathlength, their position within the covering 88 changes and they tend tomaintain their initial length, eliminating fracture from tensilestresses.

As is shown in FIGS. 11a and 11b, when the blade 90 is curved downwardsufficiently, fiber 98 (which in the unstressed blade of FIG. wasdisposed entirely above fiber 100) has moved downwardly and in part isbelow fiber 100, while fiber 100 has moved up from its initial position.Thus, although the curved length L of outside surface 94 is greater thanthe length L ofinside surface 96, fibers 98 and 100 have shifted theirpaths, between the end of the portion of blade 90 shown, to remainsubstantially at their initial unstressed length L The bundle covering88 could be held in place by any suitable mechanical means such asretention clips at regular intervals, a moderate soft epoxy or otherchemical bonding agent, or a rigid or semi-rigid chemical bonding agent.The particular holding material employed is not important. However, thebundle covering 88 must be a nonrigid material and able to conform tothe shape of the blade 90.

Referring now to FIG. 8 which shows one embodiment of the outboard endtermination of a blade using the circular bundle 86 molded into theblade, there is shown a bundle tip I02 which also may be bent up to thetop surface 104 of the blade for upshining lights which would not bevisible from the ground, bent down for down-viewing light which wouldnot be seen from above, or straight out as shown here and terminatingadjacent a Fresnel lens 106 to spread the light over a larger angle, oreven may be bifurcated or split into two or more terminations to providecoverage over a wider range.

One method of exiting the blade with the fiber bundle at the inboard end108 is illustrated in FIG. 9. The bundle 86 is shown brought out of theblade over the top surface 104 and into the region near the rotorsupport column 110 and is shown supported by clamp rings 112 which inturn are supported by a rotating portion N4 of the rotor mechanism. Thebundle 86 exits blade 90 as an integral flexible extension and extendsto the image plane as described above.

In another embodiment of the invention (FIGS. 12 through 16) the opticfibers 116 are prepared as ribbons 116 (FIG. M) of fibers each having asingle fiber or a very small number of fibers in thickness, t, and awidth, w, approximating the rotor blade width. The ribbons 116 havingindividual fibers 117 are coated with a long B state epoxy I18 (normal Bstate epoxy life is 6 to 9 months). After appropriate placement on theblade body, epoxy 118 is heat-cured and is terminated, at points 119, asufficient distance from ends 120 to 122 of the blade to permit bundlingand generation of the proper orientation of the bundle at both ends ofthe blade.

FIG. 12 illustrates the detail of the outboard end 122 of a blade 123.The blade has a core 124 about which the blade is laminated. The layersof ribbons 116 provide basic strength to the blade 123 (for example whenblade I23 bends downwardly as shown in FIG. 16) and cover the core I24.The end portions 122 of ribbons I16 extend at point 119 into an openspace from the epoxied portion of blade 123. At a position to the rightof point H9 in FIG. 12 the light fibers are separated individually (nolonger forming a ribbon) and are bunched together as a circular bundlewithin hollow cap 1128. This bundle may be split into one or morebundles I30, for example, into the three separate bundles shown. One ofthe bundles extends to the top of blade 123, one to the bottom and thethird to the outboard end 122. The blade itself is constructed of aheat-cured frame plastic with aluminum secured thereabout with epoxy.Lenses 132 are mounted on blade 123 to direct the light from the bundles130 to provide coverage in the directions desired. FIG. 13 illustratesthe termination at the inner end of the blade. The ribbons I16 aregathered together beginning at point I19 (again, the limit of the epoxyon the ribbon), from there into an inner tip hollow cap 134. A flexibleoptical bundle extension 136 having, for example, a high strengthsilicone casing which is impervious to the natural environment and isextremely flexible extends down to the image plane as described above.

As is apparent from the above description, the invention is useful inmany other applications than the lighting of helicopter navigationallights.

light, the improvement wherein said fibers are secured againstlengthwise movement along said blade and are held in a manner permittingtheir bending to accommodate vertical bending of said blade duringoperation, and a flexible light pipe extension extends from an inboardportion of said blade and in light supplying relation to said opticfibers, said light pipe extension comprising light conducting fiberportions disposed within a flexible casing portion, and being mounted torotate with said blade about the blade drive axis and adapted to flexwith repeated cyclic pivoting of said blade about the latterslongitudinal axis, said flexible light pipe extension having an endportion adapted to be held in a predetermined position relative to therotating drive mechanism of the aircraft for describing a predeterminedcircular path to sweep by and pick up light from a light source on thebody of said aircraft.

2. The rotor blade of claim 1 wherein said fibers extending along thelength of said blade comprise a flexible bundle housed in a flexiblecasing, said casing being disposed within said blade and secured againstmovement relative thereto, the internal cross-sectional area of saidcasing exceeding the aggregate cross-sectional area of said fibers ofsaid bundle, thereby providing room for said fibers to adjust themselvesrelative to one another during bending of said blade during operation.

3. The rotor blade of claim 2 wherein said light pipe extensionextending from the inboard portion of said blade is defined by anintegral extension of said fibers and casing that are within said blade.

4. The rotor blade of claim 2 wherein said optic fibers are glass fibersjoined together at their outer ends into a light transmitting endsurface by heat-resistant bonding material, said casing comprises aheat-resistant housing, and said blade comprises heat-cured structurepermanently secured about said casing.

5. The rotor blade of claim 1 wherein said optic fibers are embeddeddirectly in a structural matrix defining a portion of said blade.

6. The rotor blade of claim 5 wherein said optic fibers are glass andare secured in' a manner to contribute structural strength to saidblade.

7. The rotor blade of claim 5 wherein outboard portions of said fibersprotrude beyond said matrix into a housing, and end portions of saidfibers are bonded together to define a light transmitting face.

. 8. The rotor blade of claim 5 wherein inboard portions of said fibersprotrude beyond said matrix, forming the optic fiber portions of saidlight pipe extension.

9. The rotor blade of claim 1 wherein said fibers are secured to eachother in the form of a substantially flat ribbon, said ribbon beingbonded to other structural portions of said blade extending in thedirection of the length of said blade, with its widthwise directionextending in the direction between the leading and trailing edges ofsaid blade and the direction of its thickness aligned with the directionof operational blade bend.

10. The rotor blade of claim 9 wherein a plurality of said ribbonscomprise structural members of said blade.

111. An aircraft including the rotor blade of claim I mounted on arotating driving mechanism defining said drive axis, and a controlassembly for cyclic pivoting of said blade to alter its angle of attack,the end of said light pipe extension being secured to the rotary portionof said driving mechanism and adapted to describe a predeterminedcircular path relative to the body of the aircraft, and at least onelight source mounted on the body of the aircraft, said light sourcebeing disposed to focus light on a portion of said circular path of saidlight pipe end.

112. The aircraft of claim 1i wherein said light source includes a lensproviding a depth of focus which permits variation in tolerance of therelative positioning of said blade and said body of said aircraft.

13. The aircraft of claim 1 ll wherein said light source is defined byat least one fiber optic light pipe mounted on said body of saidaircraft, said fiber optic light pipe having a light-output end surfacepositioned to transmit a point on said circular path.

.14. In combination a rotor blade for a rotary wing aircraft havingdisposed in the body thereof a lamp, said blade having disposed thereonan element arranged to transmit light and means for supplying light fromthe inboard end of said blade to said element,

structure defining two assemblies, one movable relative to the other,and including first and second fiberoptic light pipes associatedrespectively with each assembly, the input end surface of said firstlight pipe being arranged to receive light from said lamp, the outputend surface of said first light pipe defining an object plane, the inputend surface of said second light pipe defining an image plane and theoutput end surface of said second light pipe being arranged to deliverthe transmitted light to said element, the end surfaces defining saidobject plane and said image plane being spaced apart and relativelymovable between at least one position in which they are disposed inlight transmitting alignment and at least one position in which they areout of light transmitting alignment,

and focusing structure disposed between said image and object planes andcomprising a lens assembly including a lens, said lens assembly beingspaced apart from one of said end surfaces defining one of said planes,and said lens being arranged to effectively focus light between saidobject plane and said image plane when said planes are in said lighttransmitting alignment.

15. The combination of claim 14 wherein said lens assembly is arrangedto focus, in the direction of said image plane, light from said objectplane over a region having a minimum dimension, in the direction ofrelative movement, which is substantially greater than the correspondingdimension of said input end surface of said second light pipe, saidlight transmitting alignment occurring when any portion of said regionand said input end surface of said second light pipe are aligned.

H6. The combination of claim 15 wherein one of said two relativelymovable members is a rotary member arranged to rotate relative to theother of said relatively movable members and the said output end surfaceof said second light pipe, when light is transmitted thereto, isarranged to provide a navigational light, the ratio of the magnitude ofsaid minimum dimension of said region to the perimeter of said rotatablymovable member thereby determining the portion of each revolution ofsaid rotary member during which said navigational light is energized.

17. A navigational lighting system for rotary wing aircraft, saidlighting system comprising an optic assembly including optic fibersextending along the length of each blade for conducting light from theinboard end to the outboard end thereof, an inner portion of theassembly for each blade adapted to be held in a respective predeterminedposition relative to the central rotating mechanism of the aircraft,spaced from the axis thereof for describing a predetermined circularpath, and a light source mounted on the body of the aircraftilluminating a sector of said circular path, for directing light intosaid fiber optic assembly, thence to the outer end of said assembly toprovide a navigational light.

18. The navigational lighting system of claim 17 wherein there are aplurality of light sources mounted on the body of said aircraft, eachilluminating a different sector of said circular path.

19. The navigational lighting system of claim 18 wherein there are twolight sources, one red, the other green, associated respectively withthe left and right sides of the circular path relative to the aircraft.

20. The navigational lighting system of claim 18 wherein said pluralityof light sources comprise a plurality of fiber light pipes, the outputends thereof associated with different sectors of said circular path,the input ends thereof associated with a common lamp.

21. The navigational lighting system of claim 17 wherein the circularpath for all of said blades are coincident.

22. The lighting system of claim 17 in which said light source comprisesthe combination of a lamp, a

fiber optic light pipe conducting light from the lamp to an output endsurface, and a lens assembly arranged to focus the object of said endsurface upon an image plane coincident with said path.

23. The combination of claim 22 wherein said lens assembly is arrangedto provide a light image having a depth of field sufficient to permitvariations in tolerance of the relative positioning of the output endsurface of said light pipe and the inboard end of said optic assemblywithout loss of effective transmission of light from said source to saidassembly.

24. The combination of claim 23 wherein said lens assembly has twolenses and is a Maxwellian field lens assembly.

25. The combination of claim 22 wherein the spacing between said outputend surface of said light pipe and said inboard end of said opticassembly is adapted to be one of a plurality of possible spacings and isdetermined by the installation of said combination and said lensassembly is arranged to be adjusted to conform to said ac tual spacingand thereby to effectively transmit light from said output end surfaceof said first light pipe to said inboard end of said optic assembly whensaid actual spacing is any of said plurality of possible spacings.

26. The combination of claim 22 wherein said lens assembly is arrangedto focus, in the direction of said image p ane, light rom said ob ectover a region having a dimension, in the direction of circular movementof said blade which is substantially greater than the correspondingdimension of said inboard end of said optic assembly, light transmittingalignment occurring when any portion of said region and said inboard endare aligned.

27. The combination of claim 26 wherein the ratio of the magnitude ofsaid dimension of said region to the perimeter of said circular path,determining the portion of each revolution of said rotary member duringwhich said light is transmitted is established according to aircraftnavigational rules.

1. In a rotor blade for a rotary wing aircraft, said blade including aset of optic fibers extending along the length of said blade forconducting light from an inboard end to an outboard end to providenavigational light, the improvement wherein said fibers are securedagainst lengthwise movement along said blade and are held in a mannerpermitting their bending to accommodate vertical bending of said bladeduring operation, and a flexible light pipe extension extends from aninboard portion of said blade and in light supplying relation to saidoptic fibers, said light pipe extension comprising light conductingfiber portions disposed within a flexible casing portion, and beingmounted to rotate with said blade about the blade drive axis and adaptedto flex with repeated cyclic pivoting of said blade about the latter''slongitudinal axis, said flexible light pipe extension having an endportion adapted to be held in a predetermined position relative to therotating drive mechanism of the aircraft for describing a predeterminedcircular path to sweep by and pick up light from a light source on thebody of said aircraft.
 2. The rotor blade of claim 1 wherein said fibersextending along the length of said blade comprise a flexible bundlehoused in a flexible casing, said casing being disposed within saidblade and secured against movement relative thereto, the internalcross-sectional area of said casing exceeding the aggregatecross-sectional area of said fibers of said bundle, thereby providingroom for said fibers to adjust themselves relative to one another duringbending of said blade during operation.
 3. The rotor blade of claim 2wherein said light pipe extension extending from the inboard portion ofsaid blade is defined by an integral extension of said fibers and casingthat are within said blade.
 4. The rotor blade of claim 2 wherein saidoptic fibers are glass fibers joined together at their outer ends into alight transmitting end surface by heat-resistant bonding material, saidcasing comprises a heat-resistant housing, and said blade comprisesheat-cured structure permanently secured about said casing.
 5. The rotorblade of claim 1 wherein said optic fibers are embedded directly in astructural matrix defining a portion of said blade.
 6. The rotor bladeof claim 5 wherein said optic fibers are glass and are secured in amanner to contribute structural strength to said blade.
 7. The rotorblade of claim 5 wherein outboard portions of said fibers protrudebeyond said matrix into a housing, and end portions of said fibers arebonded together to define a light transmitting face.
 8. The rotor bladeof claim 5 wherein inboard portions of said fibers protrude beyond saidmatrix, forming the optic fiber portions of said light pipe extension.9. The rotor blade of claim 1 wherein said fibers are secured to eachother in the form of a substantially flat ribbon, said ribbon beingbonded to other structural portions of said blade extending in thedirection of the length of said blade, with its widthwise directionextending in the direction between the leading and trailing edges ofsaid blade and the direction of its thickness aligned with the directionof operational blade bend.
 10. The rotor blade of claim 9 wherein aplurality of said ribbons comprise structural members of said blade. 11.An aircraft including the rotor blade of claim 1 mounted on a rotatingdriving mechanism defining said drive axis, and a control assembly forcyclic pivoting of said blade to alter its angle of attack, the end ofsaid light pipe extension being secured to the rotary portion of saiddriving mechanism and adapted to describe a predetermined circular pathrelative to the body of the aircraft, and at least one light sourcemounted on the body of the aircraft, said light source being disposed tofocus light on a portion of said circular path of said light pipe end.12. The aircraft of claim 11 wherein said light source includes a lensproviding a depth of focus which permits variation in tolerance of therelative positioning of said blade and said body of said aircraft. 13.The aircraft of claim 11 wherein said light source is defined by atleast one fiber optic light pipe mounted on said body of said aircraft,said fiber optic light pipe having a light-output end surface positionedto transmit a point on said circular path.
 14. In combination a rotorblade for a rotary wing aircraft having disposed in the body thereof alamp, said blade having disposed thereon an element arranged to transmitlight and means for supplying light from the inboard end of said bladeto said element, structure defining two assemblies, one movable relativeto the other, and including first and second fiberoptic light pipesassociated respectively with each assembly, the input end surface ofsaid first light pipe being arranged to receive light from said lamp,the output end surface of said first light pipe defining an objectplane, the input end surface of said second light pipe defining an imageplane and the output end surface of said second light pipe beingarranged to deliver the transmitted light to said element, the endsurfaces defining said object plane and said image plane being spacedapart and relatively movable between at least one position in which theyare disposed in light transmitting alignment and at least one positionin which they are out of light transmitting alignment, and focusingstructure disposed between said image and object planes and comprising alens assembly including a lens, said lens assembly being spaced apartfrom one of said end surfaces defining one of said planes, and said lensbeing arranged to effectively focus light between said object plane andsaid image plane when said planes are in said light transmittingalignment. Pg,25
 15. The combination of claim 14 wherein said lensassembly is arranged to focus, in the direction of said image plane,light from said object plane over a region having a minimum dimension,in the direction of relative movement, which is substantially greaterthan the corresponding dimension of said input end surface of saidsecond light pipe, said light transmitting alignment occurring when anyportion of said region and said input end surface of said second lightpipe are aligned.
 16. The combination of claim 15 wherein one of saidtwo relatively movable members is a rotary member arranged to rotaterelative to the other of said relatively movable members and the saidoutput end surface of said second light pipe, when light is transmittedthereto, is arranged to provide a navigational light, the ratio of themagnitude of said minimum dimension of said region to the perimeter ofsaid rotatably movable member thereby determining the portion of eachrevolution of said rotary member during which said navigational light isenergized.
 17. A navigational lighting system for rotary wing aircraft,said lighting system comprising an optic assembly including optic fibersextending along the length of each blade for conducting light from theinboard end to the outboard end thereof, an inner portion of theassembly for each blade adapted to be held in a respective predeterminedposition relative to the central rotating mechanism of the aircraft,spaced from the axis thereof for describing a predetermined circularpath, and a light source mounted on the body of the aircraftilluminating a sector of said circular path, for directing light intosaid fiber optic assembly, thence to the outer end of said assembly toprovide a navigational light.
 18. The navigational lighting system ofclaim 17 wherein there are a plurality of light sources mounted on thebody of said aircraft, each illuminating a different sector of saidcircular path.
 19. The navigational lighting system of claim 18 whereinthere are two light sources, one red, the other green, associatedrespectively with the left and right sides of the circular path relativeto the aircraft.
 20. The navigational lighting system of claim 18wherein said plurality of light sources comprise a plurality of fiberlight pipes, the output ends thereof associated with different sectorsof said circular path, the input ends thereof associated with a commonlamp.
 21. The navigational lighting system of claim 17 wherein thecircular path for all of said blades are coincident.
 22. The lightingsystem of claim 17 in which said light source comprises the combinationof a lamp, a fiber optic light pipe conducting light from the lamp to anoutput end surface, and a lens assembly arranged to focus the object ofsaid end surface upon an image plane coincident with said path.
 23. Thecombination of claim 22 wherein said lens assembly is arranged toprovide a light image having a depth of field sufficient to permitvariations in tolerance of the relative positioning of the output endsurface of said light pipe and the inboard end of said optic assemblywithout loss of effective transmission of light from said source to saidassembly.
 24. The combination of claim 23 wherein said lens assembly hastwo lenses and is a Maxwellian field lens assembly.
 25. The combinationof claim 22 wherein the spacing between said output end surface of saidlight pipe and said inboard end of said optic assembly is adapted to beone of a plurality of possible spacings and is determined by theinstallation of said combination and said lens assembly is arranged tobe adjusted to conform to said actual spacing and thereby to effectivelytransmit light from said output end surface of said first light pipe tosaid inboard end of said optic assembly when said actual spacing is anyof said plurality of possible spacings.
 26. The combination of claim 22wherein said lens assembly is arranged to focus, in the direction ofsaid image plane, lighT from said object over a region having adimension, in the direction of circular movement of said blade which issubstantially greater than the corresponding dimension of said inboardend of said optic assembly, light transmitting alignment occurring whenany portion of said region and said inboard end are aligned.
 27. Thecombination of claim 26 wherein the ratio of the magnitude of saiddimension of said region to the perimeter of said circular path,determining the portion of each revolution of said rotary member duringwhich said light is transmitted is established according to aircraftnavigational rules.